This research program has the following objectives: a) The study of the molecular and genetic determinants of the interaction between the DNA oncogenic viruses polyoma and SV40 and their host cells. For this purpose we are studying the process of integration of the viral DNA into the host cell DNA, and we are attempting to characterize the regulation of transcription of integrated and free viral genomes in different cell types. b) The study of the control of transcription and translation in cells infected or transformed by oncogenic viruses. We are attempting to study the control of transcription of SV40 genomes in an "in vitro" system of isolated nuclei, and we are studying the mechanisms and the level of translation in normal and virus transformed cells. BIBLIOGRAPHIC REFERENCES: Prasad, I., Zouzias, D., and Basilico, C. State of the viral DNA in rat cells transformed by polyoma virus, I. Virus rescue and the presence of non-integrated viral DNA molecules. J. Virol. 18, 436-444, (1976). Basilico, C. and Zouzias, D. Regulation of viral transcription and tumor antigen expression in cells transformed by simian virus 40. Proc. Nat. Acad. Sci. USA 73, 1931-1935. (1976).